(1) Field of the Invention
This invention relates to a light-emitting element. Particularly usable for emitting a white light.
(2) Related Art Statement
As a light-emitting element for illumination, a normal light source such as a incandescent lamp and fluorescent lamp and also, a light-emitting diode (LED) which is made by stacking plural semiconductor layers are used. Since a white light includes three elementary colors, and can be emitted from the incandescent lamp or fluorescent lamp, the use of the incandescent lamp or fluorescent lamp enables a given object to be observed in full color.
On the other hand, since only a monochromatic light is emitted from the LED, and determined by the structure of the LED, the full color observation can not be realized. Recently, however, a LED to emit a white light are being developed actively. For example, such a white LED as using RGB or using two elementary colors constructed of a blue LED and yellow fluorescent substances coated on the blue LED is fabricated as prototypes.
Moreover, an ultraviolet LED is fabricated and then, a white LED is fabricated as prototypes, using fluorescences from the three elementary color fluorescent substances through the irradiation of an ultraviolet beam from the ultraviolet LED. This technique is based on the principle of a fluorescent lamp, and in this case, the ultraviolet LED is used in place of mercury discharge inside the fluorescent lamp.
However, since the incandescent lamp is emitted by heating the filament, much electric power is consumed.
Moreover, since the white LED using RGB requires different LED chips, the cost rises, so that it has difficulty in making it practicable for lighting. Then, since the white LED using two elementary colors can not be used for the full color observation because it utilizes only two elementary colors, not three elementary colors. Similarly, since the white LED using the ultraviolet LED requires the fluorescent substances of the three elementary colors, separately, the cost rises. Then, if a GaN-based blue LED is modified into the ultraviolet LED so as to emit a light beam of shorter wavelength, the luminance efficiency is deteriorated remarkably.
Moreover, since the LED itself emit a light beam by utilizing a pn junction between the semiconductor layers, it has the inherent difficulty due to the pn junction control. Particularly, if such an attempt is made as to fabricate the LED of an AlGaInN-based semiconductor material, it is very difficult to fabricate a p-type semiconductor layer.
It is an object of the present invention to provide a new light-emitting element without the above-mentioned problems.
For achieving the above object, this invention relates to a light-emitting element, including a transparent substrate, a III-V nitride semiconductor layer including rare earth metal elements which is formed on the transparent substrate, and an irradiation source of electron beam which is disposed within 5 mm from the surface of the III-V nitride semiconductor layer so as to be opposite to the III-V nitride semiconductor layer, whereby the rare earth metal elements in the III-V nitride semiconductor layer are excited by electron beams from the irradiation source and a given fluorescence inherent to the rare earth metal elements are emitted.
For achieving the above object, the inventors had been intensely studied, to obtain a new light-emitting element which is different in principle and structure.
In the light-emitting element according to the present invention, since the rare earth metal elements are excited, to generate and emit a light, originated from the fluorescence of the rare earth metal elements, the chromaticity of the light can be varied freely by selecting rare each metal elements.
Also, by selecting two kinds or over of rare earth metal element and mixing them at a given ratio, the chromaticity of the light to be obtained can be varied largely.
Moreover, if Tm to generate a light within blue color wavelength region, Er to generate a light within green color wavelength region and Eu or Pr to generate a light within red color wavelength region are selected and mixed appropriately at a given ratio, the fluorescences from these rare earth metal elements are superimposed, to generate and emit a white light.
Therefore, according to the light-emitting element, the present invention, a white light can be easily generated, compared with a conventional LED. In addition, the difficulty of pn junction control which is inherent to a LED can be eliminated.
A carbon nano-tube may be adopted as the irradiation source of electron beam, and if the distance between the irradiation source and the III-V nitride semiconductor layer is set to be smaller, the light-emitting element can be illuminated below commercial voltage. Moreover, since the current required to drive the light-emitting element can be set to be extremely small, the electric power consumption can be reduced, compared with a incandescent lamp.